It is a general aim to utilize built space as efficiently as possible. For example, owing to space requirements, one aim is to make the hoisting machines of elevators as compact as possible. In order to achieve this, hoisting machines are designed to be as flat as possible in their dimensions in the direction of the axis of rotation, in which case the hoisting machines fit better in connection with, for instance, the wall part of the elevator hoistway or into some other corresponding narrow space. On the other hand, the aim in some solutions has been to design the hoisting machine so as to be as small as possible in its dimensions in the radial direction, such that the hoisting machine fits better e.g. in connection with the top end or the bottom end of the elevator hoistway.
In recent times permanent-magnet motors have started to be used in the electric motors of hoisting machines, which permanent-magnet motors comprise a concentrated stator winding that is wound into two adjacent slots around the stator tooth. In a concentrated winding the proportion of the winding overhang remains shorter than in a conventional diamond winding, in which case the size of the hoisting machine also decreases.
The use of a concentrated winding, however, causes problems. The density distribution of the magnetic flux produced by a concentrated winding in the air gap of an electric motor differs significantly from sinusoidal, and therefore contains a lot of harmonics. Harmonics, on the other hand, produce vibration and disturbing noise in a motor.